PROTOCOL: A cohort study examining the association between mirtazapine and mortality risk in adults with a diagnosis of depression

This protocol describes a cohort study comparing the risks of mortality and serious self-harm (suicide or near-fatal deliberate self-harm) between adults with depression prescribed mirtazapine, a selective serotonin reuptake inhibitor (SSRI), amitriptyline, or venlafaxine. The study is set within English primary care electronic health records from the Clinical Practice Research Datalink (CPRD) and covers the period 01 January 2005 – 30 November 2018. The study described uses an active comparator new user design: patients are included if they are first prescribed an SSRI before being prescribed mirtazapine, a different SSRI, amitriptyline, or venlafaxine as their second antidepressant. Patients are followed from the initial prescription for the second antidepressant until an outcome (mortality, serious self-harm), end of CPRD follow-up, or study end. Inverse probability of treatment weighting is used to account for confounding variables. The protocol was submitted to the CPRD Independent Scientific Advisory Committee for review and was approved in November 2019 (protocol number 19_241).